This invention relates to a process for preparing a semisolid dressing with use of soybean proteins as an emulsifier.
An increase in cholesterol in blood owing to overeating animal foods has become a serious problem and therefore, the trend of wanting foods free of cholesterol for health is rising yearly. In conventional dressings, egg yolks containing cholesterol are used as an emulsifier. Accordingly, the preparation of dressings using soybean proteins free of cholesterol instead of egg yolks is to just meet the needs of the times.
There have been, hitherto, provided mayonnaise-like foods using soybean proteins, for example, by a method of using a separated soybean protein (Reported at The 5th International Congress of Food Science and Technology, Sept. 17-22, 1978, Kyoto, Japan) or a method of subjecting soybean proteins to lactic fermentation and using the resulting lactic acid instead of vinegar (Japanese Patent Publication No. 51-32705). However, these methods are not sufficiently satisfied for the following reasons.
Soybean proteins have a good emulsifying ability, but they precipitate at a pH range of the isoelectric point because of the solubility being near zero. The conventional dressing (e.g. mayonnaise) is prepared by forming a homogeneous mixture of vinegar and egg yolk as an emulsifier, adding an edible oil and emulsifying same. In case of the egg yolk there is no problem in the emulsifying property at an acidic pH. However, in case of using soybean protein as the emulsifier, 60% or more of the soybean protein is precipitated at a pH range of the isoelectric point, even if the soybean protein is one subjected to a partial hydrolysis with an acid or enzyme to a molecular weight distribution range exhibiting a good emulsifying property. The precipitated soybean protein is extremely reduced in emulsifying ability and no longer acts as an emulsifier.
A pH range of about 4.5 which is the isoelectric point of soybean protein is included in a pH range suitable for dressing. Accordingly, the soybean protein, when mixed with vinegars, is precipitated and therefore, an emulsion of good stability cannot be obtained from a mixture of soybean proteins, vinegars and edible oils even if emulsification is effected using a powerful emulsifier. Thus, it is impossible to prepare good dressings.